Ife Journal of Science vol. 16, no. 3 (2014) 353 INTEGRATION OF HYDROGEOPHYSICAL AND REMOTE SENSING DATA IN THE ASSESSMENT OF GROUNDWATER POTENTIAL OF THE BASEMENT COMPLEX TERRAIN OF , SOUTHWESTERN .

1Bayowa O.G., 2 Olorunfemi M.O., 3 Akinluyi F.O., and 4 Ademilua O.L 1Department of Earth Sciences, Ladoke Akintola University of Technology, Ogbomoso, Nigeria. 2Department of Geology, Obafemi Awolowo University, Ile-Ife, Nigeria. 3Department of Remote Sensing and GIS, Federal University of Technology, Akure, Nigeria. 4Department of Geology, Ekiti State University, Ado-Ekiti, Nigeria. Corresponding Author E-mail:[email protected]; [email protected] (Received: 8th August, 2014; Accepted: 12th August, 2014)

ABSTRACT

Hydrogeophysical investigation as well as analyses of hydrogeomorphological, geologic/hydrogeologic, electrical resistivity and borehole data had been carried out in the Basement Complex terrain of Ekiti State, Southwestern Nigeria. This was with a view to classifying the area into different groundwater potential zones. The VES interpretation results were used for aquifer identification; aquifer geoelectric parameter determination and for the calculation of the overburden coefficient of anisotropy. Hydrogeomorphological, lineament density, lineament intersection density and overburden coefficient of anisotropy thematic maps were produced and integrated for the classification of the study area into different groundwater potential zones. The reliability of the groundwater potential map was checked with the existing groundwater yield data. The weathered and fractured basement constituted the main aquifer units. The groundwater yields of boreholes located within quartzitic rocks had a mean of 1.56 l/s while the mean groundwater yield from metasediment (schist) was 1.14 l/s. The study area was characterized into five different groundwater potential zones which were very low, low, moderate, high and very high. Ijelu-Ekiti, Ayede, Ipao, , Oye. Ayegbaju, Ofale-Ijero and Omuo-Ekiti were classified as very low groundwater potential areas while low groundwater potential was established in Ijesa-Isu, Iludofin, Iyemero, Esure, Otun, Osi, Iropora, Ifaki, Ikun, Ijero, Ado, and Ise/Orun. Igbara-Odo, Ilawe, Ikogosi, Ido, Ipole-Iloro, Ipere, Ayetoro, Ikoro, Ifisin, Ilogbo, Isinbode, Erinmope and Iwaro fall within moderate groundwater potential zones. High groundwater potential was recorded in Ijan, Okemesi, Aramoko, Ilemeso, Ikere, Etisun and Itawure. -Alaaye and Ilumoba fall within very high groundwater potential zone. The groundwater potential of Ekiti State is generally of very low–moderate level rating. There were however few areas with high to very high groundwater potential.

Keywords: Basement Complex, Hydrogeophysics, Remote Sensing, Groundwater Potential, Ekiti State.

INTRODUCTION anisotropy and groundwater yield in the basement There has been a progressive increase in the complex area of the southwestern Nigeria. Their population of Ekiti State with the attendant findings include amongst others that the increase in the demand for potable water for both groundwater yield generally increases with domestic and industrial usages. The gross increase in the overburden coefficient of inadequacy of public water supply has made anisotropy. Teme and Oni (1991) used remote groundwater development through hand dug wells sensing techniques to detect groundwater flow in and boreholes inevitable. However, the success of fractured media in hard rock terrain. They used groundwater development programme is aerial photographs and radar imageries to predicated on good understanding of the adequately locate and delineate the extent and geomorphological, geological, hydrogeological frequency of these fractured systems thus making and geophysical characteristics of the basement it possible for the siting of productive boreholes at complex terrain. These characteristics are required approximately predetermined localities within the for the assessment of the groundwater potential. basement areas. Mohammed (1992) carried out a Groundwater investigation is therefore often geophysical investigation for groundwater multidisciplinary in approach and could involve development at the Federal University of terrain analysis, geology/hydrogeology, remote technology, Akure.His conclusion was that deep sensing and geophysics. Olorunfemi et al., (1991) weathered zones and fractured or brecciated investigated the relationship between electrical basement which are characterized by relatively low 354 Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater resistivity values constitute the main aquifer unit in mainly an upland zone rising over 250 metres the area. Salem (1999) submitted that fluid above the sea level and has a rhythmically transmissivity (layer thickness x permeability) and undulating surface. The area enjoys tropical electric transverse resistance (layer thickness x climate with high rainfall of up to 1600 mm and is resistivity) are important parameters in characterized by two distinct seasons (Ayoade groundwater and hydrocarbon exploration. The 1988). These are the rainy season (April-October) and the dry season (November-March). determination of these parameters provides a o o good knowledge of the potential of porous media, Temperature ranges between 21 and 28 C. The because they relate fluid flow to electric current mean monthly relative humidity is less than 70%. conduction in terms of layer thickness, The South-Westernly wind and the North-East permeability and resistivity. The author Trade wind blows during the rainy and dry established a direct relationship between fluid (Harmattan) season respectively (http://ekitinigeria.net). The vegetation of the area transmissivity and the electric transverse is the rain forest type. Tropical forest exists in the resistance, with coefficients of correlation of 0.99 south. This is characterized by dense evergreen (for aquifers) and 0.94 (for reservoirs) and forest of tall trees with thick vegetation. However, suggested that an increase in both parameters Guinea Savannah occupies the northern indicate presence of zones of high fluid potential periphery (http://ekitinigeria.net). within the aquifers and the reservoirs. Ademilua (1997) attempted to classify both Ondo and Ekiti Geology States into different groundwater potential zones The study area is underlain by the Precambrian but was constrained by few VES data points as well rocks of the Basement Complex of Southwestern as limited sampled localities. Hence, the Nigeria (Figure 2). The basement rocks are groundwater potential map produced by the concealed in places by a variably thick overburden. researcher could not have been representative. A The major lithologic units according to Rahaman preliminary assessment of the groundwater (1976, 1988) are the migmatite-gneiss complex; potential based on terrain and satellite imagery the older granites; the charnockitic rocks; the analyses had been undertaken by Bayowa et al., slightly migmatised to unmigmatised paraschists 2014b. There is therefore the need for detailed and metaigneous rocks and the assessment of the groundwater potential using unmetamorphosed granitic rocks. The migmatite- integrated hydrogeomorphological, gneiss complex is composed mainly of early ,geological/hydrogeological (involving recent gneiss, mafic and ultramafic bands and the granitic satellite imageries covering state) and geophysical or felsic components. The rock type is the most data acquired across the state. widespread, covering about half of the study area (Figure 3). The older granites comprise the The Study Area porphyritic-biotite granite and the medium-coarse The study area lies within Latitudes 7º 15' 00" and grained granite gneiss. The charnockitic rocks are 8º 10' 00" North of the Equator and Longitudes 4º composed of quartz, alkali feldspars, plagioclase, 45' 00" and 5º 50' 00" East of the Greenwich orthopyroxene, clinopyroxene, hornblende, Meridian. Ekiti State has 16 Local Government biotite and accessory amount of opaque ore Areas (Figure 1). Some of the major towns in apatite, zircon and allanite. The slightly Ekiti-State include Ado-Ekiti, Efon-Alaaye, migmatised to unmigmatised paraschists and Aramoko, Ikole, Ikere, Ijero, Ise, Otun, Ido, metaigneous rocks consist of pelitic schists, Emure, Ifaki, Iyin, Igede, Ilawe, Ode, Oye, Omuo, quartzites, amphibolites, talcose rocks, Ilupeju, Ikoro, Igogo, Iye, Ijesa-Isu, Ayedun, metaconglomerates, marbles and calc-silicate Okemesi, Igbara-Odo, etc. Its capital is located at rocks. The umetamorphosed granitic rocks Ado-Ekiti. manifest as dolerite dykes, pegmatites and quartz veins. Physiographically, the state is composed of hilly terrain and Plains with isolated hill locks. According to http://ekitinigeria.net, the area is Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater 355

Figure 1: Map of Ekiti State showing the Local Government Areas. (Digitized from Administrative Map of Ekiti State, 2000).

Figure 2: Geological Map of Nigeria (Digitized from Ajibade and Umeji, 1989) 356 Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater

Figure 3: Geologic Map of Ekiti-State (Digitized from Ademilua, 1997)

Hydrogeology of water into larger river valleys. Within the The hydrogeology of an area is controlled by such weathered zone, discontinuous water table occurs factors as geology, structures and climate of an and water level shows marked seasonal area (Ademilua, 1997). This is because the fluctuations (Dan-Hassan, 1993). The highest geological formations underlying the area and the groundwater yield in basement terrains is found in structures determine the types of aquifer and the areas where thick overburden overlies fractured means of recharging them while the climate zones (Olorunniwo and Olorunfemi, 1987; determines the amount and rate of recharge of the Olorunfemi. and Fasuyi, 1993). aquifer (Mailu, 1987; Lewis, 1987; Shemang, 1990). The hydrogeology of an area is considered Methodology under two aspects: (i) surface water and (ii) Borehole logs and other ancillary information in groundwater. The major surface waters in the the study area were secured from various archives study area are rivers Ogbese, Osun, Oni, Osse and and reputable drillers. Parametric Vertical Ero and their tributaries (Figure 3). The water Electrical Sounding (VES) were carried out on the below the watertable is generally called the forty (40) existing boreholes, using the groundwater. Groundwater is contained in pore Schlumberger electrode array. The VES data were spaces of sediments and in weathered and interpreted quantitatively by partial curve fractured basement columns (Bayowa et al. matching and 1-D computer assisted forward (2014a). Wells dug close to the river normally modelling. The overburden coefficient of contain groundwater at shallow depths Shemang anisotropy (ë) was calculated for all the parametric (1990). However, the water table falls VES points to the drilled boreholes and related to progressively throughout the dry season. the borehole yield. The hydrogeomorphological, Generally, the closer a well is to the river channel, lineament density, lineament intersection density the smaller the fall. This lowering of the water and the coefficients of anisotropy thematic maps table is mainly controlled by subsurface movement were integrated for the classification of the study Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater 357 area into groundwater potential zones. Borehole Figure 4 shows the superposition of borehole yield data were used to validate the final site/yield on the solid geology in the study area. groundwater potential map. The borehole yield from charnockite underlain areas vary between 0.35 l/s and 1.50 l/s with a RESULTS AND DISCUSSION mean value of 0.93 l/s while that from metamorphic rocks ranges from 0.1 l/s to 4.1 l/s. Relationship between Groundwater Yield, with a mean value of 1.47 l/s. The groundwater Geology, Lineament and Lineament Density. yields of boreholes located on quartzitic rocks Borehole yield values obtained in the study area have a mean of 1.56 l/s. The mean groundwater ranged between 0.1 l/s and 4.1 l/s. Five (5) yields for metasediment (schist) is 1.14 l/s. The different aquifer combinations which include the relatively high mean groundwater yield value weathered, weathered/partly weathered/fractured obtained on the quartzitic rocks may not be (unconfined), weathered/fractured (confined), unconnected with the high fracture (lineament) weathered/fractured(unconfined)/fractured density. Figures 5 and 6 respectively show (confined) and fractured(confined) aquifer superposition of borehole points/yields on the systems were identified from the analysis of the lineament and lineament intersection density borehole completion records. The overburden maps of the study area. The average borehole thickness for areas underlain by charnockite is yield on, close to and outside the lineament and between 2.6 m and 41.6 m with a mean value of lineament intersections are 1.20, 1.21 and 0.88 l/s 22.1 m while for areas underlain by metamorphic and 1.20, 1.50 and 0.89 l/s respectively. This rocks, the range is between 0.9 m and 71.1 m with a analysis shows that boreholes located on or close mean value of 36 m. The borehole depths for areas to lineament and or lineament intersection have underlain by charnockite range from 19 m to 48 m relatively high groundwater yield. This deduction with an average value of 33.5 m. while for areas is corroborated by the findings of Edet (1996). underlain by metamorphic rocks, the range is Edet et al. (1994) and Edet and Okereke (1997). between 21 m and 35 m with a mean of 28 m.

Figure 4: Superposition of Borehole Points on the Solid Geology. 358 Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater

Figure 5: Superposition of Borehole Points/Yields on Hydro-Lineament Map.

Figure 6: Superposition of Borehole Points/Yields on Lineament Intersection Map. Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater 359 Relationship Between Overburden borehole yield values were cross plotted as shown Coefficient of Anisotropy and Groundwater in Figure 7. The figure shows a weak linear Yield. correlation between groundwater yield and In an attempt to partition the study area into coefficient of anisotropy with correlation different groundwater potential zones, the coefficient of 0.6. coefficient of anisotropy (ë) was calculated for each of the parametric VES to the drilled Classification of Borehole Yield in terms of boreholes in the study area. The value for the Groundwater Potential. electrical coefficient of anisotropy (ë) for each of The groundwater yield of a basement complex the drilled borehole localities ranges between 1.00 area can be classified in terms of groundwater and 1.60 units. The values obtained in the present potentials as shown in Table 1. Borehole yields in study fall within the range obtained for areas the range of 0.1 – 1.0 l/s are classified as low underlain by metamorphic rocks in the (Carruthers and Smith, 1992). The subsequent southwestern part of Nigeria (Olorunfemi et al., classifications were aided by Olorunfemi (2008) 1991). The coefficients of anisotropy and and groundwater yield data spread on Figure 7.

Figure 7: Coefficient of Anisotropy versus Groundwater Yield Parametric Cross Plot for the Study area.

Table 1: Classification of Borehole Yield in terms of Groundwater Potential in the Basement Complex area of Ekiti State (Adapted from: Carruthers and Smith 1992, Olorunfemi, 2008 and Field Experience)

Borehole Yield Range (l/s) Groundwater Potential

0 – 0.49 Very Low

0.5 – 0.99 Low

1.0 – 1.49 Moderate

1.5 – 2.5 High

> 2.5 Very High 360 Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater Groundwater Potential Evaluation of the Oye. Ayegbaju, Ofale-Ijero and Omuo-Ekiti are Study Area characterized by very low groundwater potential To classify the basement complex area of Ekiti- while low groundwater potential is observed in State into different groundwater potential zones, areas around Ijesa-Isu, Iludofin, Iyemero, Esure, the following geologic and geoelectric parameters Otun, Osi, Iropora, Ifaki, Ikun, Ijero, Ado, Emure have been integrated in ArcGIS environment.(i) and Ise/Orun. It is evident from the map that Hydrogeomorphic Conditions,(ii) Hydrogeologic areas around Igbara-Odo, Ilawe, Ikogosi, Ido, Lineament Density Distribution, (iii) Lineament Ipole-Iloro, Ipere, Ayetoro, Ikoro, Ifisin, Ilogbo, Intersection Density Distribution and (iv) Isinbode, erinmope and Iwaro are characterized Electrical Coefficient of Anisotropy. By applying by moderate groundwater potential. High a trial and error method, the weighted indices in groundwater potential is expected in areas around Table 2 (a-d) were used to integrate the Ijan, Okemesi, Aramoko, Ilemeso, Ikere, Etisun hydogeomorphological, lineament density, and Itawure. Efon-Alaaye and Ilumoba fall within Lineament intersection density and the electrical the very high groundwater potential zone. Figure coefficient of anisotropy thematic maps. Four 9 shows the superposition of borehole yields on different groundwater potential maps were the final groundwater potential map. A generated and the reliability of each map was generalized groundwater potential rating was checked with the existing groundwater yield data subsequently carried out for each local and the classification in Table 1. Percentage government area in the study. Moba and Oye reliability of 47%, 38%, 56% and 70% respectively Local Government Areas have generally very low were obtained for the first – fourth trial for groundwater potential rating. Ekiti-East, Ido-Osi, correlation between the groundwater yield data Ikole and Irepodun-Ifelodun Local Government and the groundwater potential map generated. Areas are characterized by generally low The fourth weighting combination (Table 2d) groundwater potential. Ado-Ekiti, Emure, Ekiti which gave the highest correlation of 70% was South-West, Ekiti-West, Ijero, Ikere, and adopted in this study and resulted in the Ise-Orun Local Government Areas have generally groundwater potential map displayed in Figure 8. moderate groundwater rating. However, The map classifies the study area into very low, low, and Efon Local Government areas are moderate, high and very high groundwater characterized by generally high groundwater potential zones. The groundwater map shows that potential. localities such as Ijelu-Ekiti, Ayede, Ipao, Ikole,

Table 2: Development of Weighted Index for the Parameters used for Groundwater Potential Map

Parameters Weighted Index (%)

Hydrogeomorphic 10 Lineaments Density 40 Lineament Intersections Density 30 Coefficient of Anisotropy 20 (a) First Trial (Percentage Correlation = 47%)

Parameters Weighted Index (%)

Hydrogeomorphic 10 Lineaments Density 35 Lineament Intersections Density 25 Coefficient of Anisotropy 30

(b) Second Trial (Percentage Correlation = 38%) Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater 361

Parameters Weighted Index (%) Hydrogeomorphic 05 Lineaments Density 30 Lineament Intersections Density 15 Coefficient of Anisotropy 50 (c) Third Trial (Percentage Correlation = 56%) Parameters Weighted Index (%) Hydrogeomorphic 05 Lineaments Density 50 Lineament Intersections Density 30 Coefficient of Anisotropy 15 (d) Fourth Trial (Percentage Correlation = 70%)

Figure 8: Groundwater Potential Map of the Study Area.

Figure 9: Superposition of the Borehole Yields/Points on Groundwater Potential Map of the Study Area. 362 Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater Limitation of Groundwater Potential Map Ayoade J. O. 1988. Tropical hydrology and The groundwater potential map gives a regional water Resources. Macmillan Publishers over view of the groundwater potential of the Ltd, London and Basingstoke, pp. 5-7, basement complex area of Ekiti State. The Siting Boreholes. Groundwater 26, 54-63 heterogeneous and discontinuous nature of Bayowa G. O. Olorunfemi M. O. and Ademilua O. basement aquifers makes local variation possible. L. 2014a. A Geoelectric Assessment and Classification of the aquifer systems in a CONCLUSIONS Typical Basement Complex Terrain: Case The groundwater potential map shows that the study of Ekiti State, Southwestsern study area can be classified into five different Nigeria. Research Journal in Engineering and groundwater potential zones which are very low, Applied Sciences 3 (1) 55- 60. low, moderate, high and very high. Ijelu-Ekiti, Bayowa O. G., Olorunfemi, M. O., Akinluyi, F. O., Ayede, Ipao, Ikole, Oye. Ayegbaju, Ofale-Ijero and and Ademilua, O. L. 2014b. A Preliminary Omuo-Ekiti are located within the very low Assessment of the Groundwater groundwater potential zone. Low groundwater Potential of Ekiti State, Southwestern potential zone covers areas such as Ijesa-Isu, Nigeria, using Terrain and Satellite Iludofin, Iyemero, Esure, Otun, Osi, Iropora, Imagery Analyses. In Press. Ifaki, Ikun, Ijero, Ado, Emure and Ise/Orun. Carruthers, A.M. and Smith, I.F. 1992. The use of Igbara-Odo, Ilawe, Ikogosi, Ido, Ipole-Iloro, ground Electrical Methods for siting Ipere, Ayetoro, Ikoro, Ifisin, Ilogbo, Isinbode, Water Supply boreholes in shallow Erinmope and Iwaro are located within moderate Crystalline Basement Terrains. In: Wright, groundwater potential zone. Ijan, Ilumoba, E.P and Burgess, W.G. (eds.), The Okemesi, Efon-Alaaye, Aramoko, Ilemeso, Ikere, hydrogeology of crystalline Basement Aquifers in Etisun and Itawure fall within the high to very high Africa. Special Publication 66, Geological potential zone. Moba and Oye Local Government Society London. pp. 183-230. Areas are located within very low groundwater Dan-Hassan, M. A. 1993. Combined potential. Ekiti-East, Ido-Osi, Ikole and Electromagnetic and Electrical Resistivity Irepodun-Ifelodun Local Government Areas are Survey for Groundwater development in characterized by generally low groundwater North Central part of Kaduna State. potential. Ado-Ekiti, Emure, Ekiti South-West, Unpubli. M.Sc. Thesis, Geology Department, Ekiti-West, Ijero, Ikere, Ilejemeje and Ise-Orun Obafemi Awolowo University, Ile-Ife, Nigeria. Local Government Areas have generally moderate pp. 1 – 107. groundwater potential rating. However, Gbonyin Edet, A. E. 1996. 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